US Airways initiated the fare increase late Thursday on most routes. Delta Air Lines later followed, mostly on routes where it competes with discount airlines. JetBlue and Virgin America have already matched the increase, airline analyst Jaime Baker said Friday. JetBlue also extended the travel period for the increases to include dates before and after the peak summer travel season.

AirTran is also raising fares on some routes, not including those to and from Atlanta, where it competes with Delta. This is the first time AirTran has attempted a major fare increase in several months, Baker noted.

Airlines have tried widespread price increases nine times this year. Six stuck. The last three failed within days because other airlines didn’t raise prices too. One way to tell if the latest attempt will be successful is if Southwest Airlines joins in and raises fares. It carries more passengers than any other airline in the U.S. and also regularly undercuts the major airlines’ fares. The airlines also accounts for more than half of the market share at Baltimore-Washington International Marshall Airport.

Oil is now above $110 per barrel, having risen 21 percent so far this year. Fare watcher Rick Seaney points out that the airlines successfully raised prices four times in April 2008 when oil prices rose from $102 to $117. Oil has already gained more than $4 per barrel this month.

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